Oligothiophene-arylene derivatives and organic thin film transistors using the same

ABSTRACT

An oligothiophene-arylene derivative wherein an arylene having n-type semiconductor characteristics is introduced into an oligothiophene having p-type semiconductor characteristics, thereby simultaneously exhibiting both p-type and n-type semiconductor characteristics. Further, an organic thin film transistor using the oligothiophene-arylene derivative.

This application is a DIV of 11/084,794 filed Mar. 21, 2005 now U.S.Pat. No. 7,541,424.

This non-provisional application claims priority under 35 U.S.C. §119(a)on Korean Patent Application No. 2004-83618 filed on Oct. 19, 2004,which is herein expressly incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

Embodiments of the present invention relate to an oligothiophene-arylenederivative and an organic thin film transistor using the derivative.More particularly, embodiments of the present invention relate to anoligothiophene-arylene derivative wherein an arylene having n-typesemiconductor characteristics is introduced into an oligothiophenehaving p-type semiconductor characteristics, thereby simultaneouslyexhibiting both p-type and n-type semiconductor characteristics.

2. Description of the Related Art

General organic thin film transistors (OTFTs) comprise a substrate, agate electrode, an insulating layer, source/drain electrodes, and achannel layer. Organic thin film transistors are classified intobottom-contact (BC) OTFTs wherein a channel layer is formed on sourceand drain electrodes, and top-contact (TC) OTFTs wherein metalelectrodes are formed on a channel layer by mask deposition.

Inorganic semiconductor materials, such as silicon (Si), have beencommonly used as materials for channel layers of TFTs. However, sincethe preparation of such inorganic semiconductor materials involves highcosts and requires a high-temperature vacuum process to fabricate TFTs,organic semiconductor materials currently replace inorganicsemiconductor materials in order to fabricate large area, flexibledisplays at reduced costs.

Recently, studies on organic semiconductor materials for channel layersof OTFTs have been actively undertaken and the characteristics of thedevices have been reported. Of these, a great deal of research iscurrently concentrated on low molecular weight materials and oligomers,e.g., phthalocyanines, perylenes, pentacenes, C60, thiophene oligomers,and the like. Lucent Technologies Inc. and 3M Inc. developed deviceswith charge carrier mobilities as high as 3.2-5.0 cm²/Vs using apentacene (Mat. Res. Soc. Symp. Proc. 2003, Vol. 771, L6.5.1-L6.5.11).In addition, CNRS, France, reported a device having a relatively highcharge carrier mobility of 0.01-0.1 cm²/Vs and a relatively high on/offcurrent ratio (I_(on)/I_(off) ratio) using an oligothiophene derivative(J. Am. Chem. Soc., 1993, Vol. 115, pp. 8716-9721).

However, since the prior art devices are largely dependent on vacuumprocesses for thin film formation, the fabrication of the devices incursconsiderable costs.

On the other hand, high molecular weight-based organic thin filmtransistors (charge carrier mobility: 0.01-0.02 cm²/Vs) employing apolythiophene-based material (F8T2) have already been fabricated andtested (PCT Publication WO 00/79617, Science, 2000, vol. 290, pp.2132-2126). U.S. Pat. No. 6,107,117 discloses the fabrication of anorganic thin film transistor with a charge carrier mobility of 0.01-0.04cm²/Vs by employing polythiophene P3HT, which is a representativeregioregular polymer.

Since the regioregular polythiophene P3HT shows a charge carriermobility of about 0.01 cm²/Vs but a high off-state leakage current (10⁻⁹A or more), leading to a low I_(on)/I_(off) ratio of 400 or less, it isnot applicable to the fabrication of electronic devices.

Low molecular weight organic semiconductor materials for organic thinfilm transistors that can be spin-coated at room temperature andsimultaneously satisfy the requirements of high charge carrier mobilityand low off-state leakage current, have not hitherto been reported.

SUMMARY OF THE INVENTION

Therefore, embodiments of the present invention have been made in viewof the above problems of the prior art, and it is an object ofembodiments of the present invention to provide anoligothiophene-arylene derivative wherein an arylene having n-typesemiconductor characteristics is introduced into an oligothiophene unithaving p-type semiconductor characteristics, thereby enablingspin-coating at room temperature and simultaneously exhibiting both highcharge carrier mobility and low leakage current.

In accordance with one aspect of the present invention, there isprovided an oligothiophene-arylene derivative represented by Formula 1below:

wherein

Ar is a C₂₋₃₀ heteroarylene interrupted by at least one nitrogen atomwhich may be substituted with hydrogen, hydroxyl, amino, C₁₋₂₀ linear,branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, ester or amido,or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, ester or amido;

Ar₁ is a C₂₋₃₀ aryl group which may be interrupted by at least oneheteroatom and may be substituted with hydrogen, hydroxyl, amino, C₁₋₂₀linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, esteror amido, or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, esteror amido;

Ar₂ is a C₅₋₃₀ aryl group which may be interrupted by at least oneheteroatom and may be substituted with hydrogen, hydroxyl, amino, C₁₋₂₀linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, esteror amido, or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, esteror amido;

the substituents R₁ are each independently hydrogen, hydroxyl, amino,C₁₋₂₀ linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino,ester, amido, or a C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino,ester or amido;

n₂ is an integer between 2 and 8; and

n₁ and n₃ are each independently an integer between 0 and 6.

In accordance with another aspect of the present invention, there isprovided an organic thin film transistor in which the oligomer materialis used as a material for an organic active layer, thereby enablingspin-coating at room temperature and simultaneously satisfying therequirements of high charge carrier mobility and low off-state leakagecurrent.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages ofembodiments of the present invention will be more clearly understoodfrom the following detailed description taken in conjunction with theaccompanying drawings, in which:

FIG. 1 is a cross-sectional view showing the structure of a devicefabricated in Example 1;

FIG. 2 is a ¹H-NMR spectrum of an oligothiophene-arylene derivativeprepared in Preparative Example 7;

FIG. 3 is a ¹H-NMR spectrum of an oligothiophene-arylene derivativeprepared in Preparative Example 11;

FIG. 4 is a graph showing the current transfer characteristics of anorganic thin film transistor fabricated in Example 1 using anoligothiophene-arylene derivative prepared in Preparative Example 7; and

FIG. 5 is a graph showing the current transfer characteristics of anorganic thin film transistor fabricated in Example 5 using anoligothiophene-arylene derivative prepared in Preparative Example 11.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail.

The oligothiophene-arylene derivative of the present invention isrepresented by Formula 1 below:

wherein

Ar is a C₂₋₃₀ heteroarylene interrupted by at least one nitrogen atomwhich may be substituted with hydrogen, hydroxyl, amino, C₁₋₂₀ linear,branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, ester or amido,or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, ester or amido;

Ar₁ is a C₂₋₃₀ aryl group which may be interrupted by at least oneheteroatom and may be substituted with hydrogen, hydroxyl, amino, C₁₋₂₀linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, esteror amido, or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, esteror amido;

Ar₂ is a C₅₋₃₀ aryl group which may be interrupted by at least oneheteroatom and may be substituted with hydrogen, hydroxyl, amino, C₁₋₂₀linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, esteror amido, or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, esteror amido;

the substituents R₁, are each independently hydrogen, hydroxyl, amino,C₁₋₂₀ linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino,ester, amido, or a C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino,ester or amido;

n₂ is an integer between 2 and 8; and

n₁ and n₃ are each independently an integer between 0 and 6.

The oligothiophene-arylene derivative of embodiments of the presentinvention is synthesized from compounds of Formulae 2, 3, 4 and 5 below:X₁—Ar—X₂  Formula 2

wherein

Ar is as defined in Formula 1, and

X₁ and X₂ are each independently Br, Cl, or I;

wherein

Ar₁ is as defined in Formula 1,

X₃ is a trialkyltin group, a dioxaborane group, boronic acid, or thelike, and

n₁ is an integer between 0 and 6;

wherein

X₄ is a trialkyltin group, a dioxaborane group, boronic acid, or thelike, and

n₂ is an integer between 2 and 8; and

wherein

Ar₂ is as defined in Formula 1,

X₅ is a trialkyltin group, a dioxaborane group, boronic acid, or thelike, and

n₃ is an integer between 0 and 6.

In the oligothiophene-arylene derivative of Formula 1 according toembodiments of the present invention, non-limiting representativeexamples of compounds corresponding to Ar include compounds representedby Formula 6 below:

wherein

R₂, R₃ and R₄ are each independently hydrogen, hydroxyl, amino, C₁₋₂₀linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, ester,amido, or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, ester oramido.

Specific examples of the compounds of Formula 6 include, but are notlimited to, thiadiazoles, oxazoles, isoxazoles, oxadiazoles, imidazoles,pyrazoles, thiadiazoles, triazoles, tetrazoles, pyridines, pyridazines,pyrimidines, pyrazines, triazines, quinolines, isoquinolines,quinoxalines, naphthyridines, benzoimidazoles, pyrimidopyrimidines,benzothiadiazoles, benzoselenadiazoles, benzotriazoles, benzothiazoles,benzoxazoles, phenanthrolines, phenazines, and phenanthridines.

In the oligothiophene-arylene derivative of Formula 1 according toembodiments of the present invention, non-limiting representativeexamples of compounds corresponding to Ar₁ include compounds representedby Formula 7 below:

wherein

R₅, R₆, R₇, R₈, R₉, R₉, R₁₀, R₁₁, R₁₂ and R₁₃ are each independentlyhydrogen, hydroxyl, amino, C₁₋₂₀ linear, branched or cyclic alkyl, C₁₋₂₀alkoxyalkyl, alkylamino, ester, amido, or C₁₋₁₆ linear, branched orcyclic alkoxy, alkylamino, ester or amido.

Specific examples of the compounds of Formula 7 include, but are notlimited to, thiophenes, thiazoles, thiadiazoles, oxazoles, isoxazoles,oxadiazoles, imidazoles, pyrazoles, thiadiazoles, triazoles, tetrazoles,pyridines, pyridazines, pyrimidines, pyrazines, triazines, quinolines,isoquinolines, quinoxalines, naphthyridines, benzoimidazoles,pyrimidopyrimidines, benzothiadiazoles, benzoselenadiazoles,benzotriazoles, benzothiazoles, benzoxazoles, phenanthrolines,phenazines, phenanthridines, benzenes, naphthalenes, and fluorenes.

In the oligothiophene-arylene derivative of Formula 1 according toembodiments of the present invention, non-limiting representativeexamples of compounds corresponding to Ar₂ include compounds representedby Formula 8 below:

wherein

R₁₄, R₁₅, R₁₆, R₁₇, R₁₈, R₁₉, R₂₀ and R₂₁ are each independentlyhydrogen, hydroxyl, amino, C₁₋₂₀ linear, branched or cyclic alkyl, C₁₋₂₀alkoxyalkyl, alkylamino, ester, amido, or C₁₋₁₆ linear, branched orcyclic alkoxy, alkylamino, ester or amido.

Specific examples of the compounds of Formula 8 include, but are notlimited to, C₅₋₃₀ aromatic compounds, for example, benzenes,naphthalenes, anthracenes, and fluorenes.

The oligothiophene-arylene derivative of embodiments of the presentinvention can be synthesized by chemical or electrochemical oxidationand condensation using an organometallic compound of a transition metal,such as nickel or palladium. More preferably, the oligothiophene-arylenederivative of embodiments of the present invention can be synthesized bycondensation using a palladium (0) compound of Formula 9, or a palladium(II) compound of Formula 10 or 11 below:Pd(L)₄  Formula 9

wherein L is a ligand selected from the group consisting oftriphenylphosphine (PPh₃), triphenylarsine (AsPh₃), triphenylphosphite(P(OPh)₃), diphenylphosphinoferrocene (dppf), diphenylphosphino butane(dppb), acetate (OAc), and dibenzylideneacetone (dba);Pd(L)₂(X)₂  Formula 10

wherein L is as defined in Formula 9, and X is I, Br or Cl; orPd(L)₂  Formula 11

wherein L is as defined in Formula 9.

The condensation is carried out through the reaction paths depicted bythe following Reaction Scheme 1:

Specifically, the condensation is carried out under a nitrogenatmosphere at 70-130° C. for 2-24 hours by the Suzuki coupling reactiongenerally known in the art. At this time, toluene, dimethoxy ether,tetrahydrofuran, dimethylformamide, water, etc., can be used as asolvent.

Non-limiting, representative examples of oligothiophene-arylenederivatives that can be synthesized by the Suzuki coupling reactioninclude compounds 1, 2, 3, 4, and 5 of Formula 12 below:

To synthesize the oligothiophene-arylene derivatives of Formula 12,dihalide-substituted arylene derivatives (e.g., the compound of Formula2) and boron-substituted compounds (e.g., the compounds of Formulae 3 to5) are necessary. Compounds that are actually used to prepare theoligothiophene-arylene derivatives of Formula 12 in the presentinvention are the compounds 6, 7, 8 and 9 represented by Formula 13 andthe compounds 10, 11, 12 and 13 of Formula 14 below:

The oligothiophene-arylene derivative of embodiments of the presentinvention can be used as a novel organic semiconductor material for anactive layer of an OTFT. General organic thin film transistors havestructures of a substrate/a gate electrode/a gate insulating layer/anorganic active layer/source-drain electrodes, a substrate/a gateelectrode/a gate insulating layer/source-drain electrodes/an organicactive layer, and the like, but are not limited to these structures.

At this time, the oligothiophene-arylene derivative of embodiments ofthe present invention can be formed into a thin film by screen printing,printing, spin coating, dipping, or ink spraying.

The gate insulating layer constituting the OTFT can be made of commoninsulators having a high dielectric constant. Specific examples ofsuitable insulators include, but are not limited to, ferroelectricinsulators, e.g., Ba_(0.33)Sr_(0.66)TiO₃ (BST), Al₂O₃, Ta₂O₅, La₂O₅,Y₂O₃, and TiO₂; inorganic insulators, e.g., PbZr_(0.33)Ti_(0.66)O₃(PZT), Bi₄Ti₃O₁₂, BaMgF₄, SrBi₂(TaNb)₂O₉, Ba(ZrTi)O₃ (BZT), BaTiO₃,SrTiO₃, Bi₄Ti₃O₁₂, SiO₂, SiN_(x), and AION; and organic insulators,e.g., polyimides, benzocyclobutenes (BCBs), parylenes, polyacrylates,polyvinylalcohols, polyvinylphenols, and the like.

The substrate constituting the organic thin film transistor can be madeof, but is not limited to, glass, polyethylenenaphthalate (PEN),polyethyleneterephthalate (PET), polycarbonate, polyvinylalcohol,polyacrylate, polyimide, polynorbornene, polyethersulfone (PES), and thelike.

The gate electrode constituting the organic thin film transistor can bemade of common metals. Specific examples of such metals include, but arenot limited to, gold (Au), silver (Ag), aluminum (Al), nickel (Ni),indium tin oxide (ITO), and the like.

The source and drain electrodes constituting the organic thin filmtransistor can be made of common metals. Specific examples of suchmetals include, but are not limited to, gold (Au), silver (Ag), aluminum(Al), nickel (Ni), indium tin oxide (ITO), and the like.

Embodiments of the present invention will now be described in moredetail with reference to the following examples. However, these examplesare given for the purpose of illustration and are not to be construed aslimiting the scope of the invention.

Preparative Example 1 Preparation of Arylene 6

A catalytic amount of acetic acid was added to1,2-diamino-3,6-dibromobenzene and 2,2′-thenil in butanol. The mixturewas heated to 110° C. for 8 hours. The resulting mixture was allowed tocool to room temperature, and filtered with washing (methanol),affording the arylene 6 as a red solid.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 7.04 (t, 2H, J=5.0 Hz), 7.48 (d, 2H,J=5.0 Hz), 7.55 (d, 2H, J=5.0 Hz), 7.82 (s, 2H).

Preparative Example 2 Preparation of Arylene 7

A catalytic amount of acetic acid was added to3,4-diamino-2,6-dibromopyridine and 2,2′-thenil in butanol. The mixturewas heated to 110° C. for 8 hours. The resulting mixture was allowed tocool to room temperature, and filtered with washing (methanol),affording the arylene 7 as an ocher solid.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 7.06-7.10 (m, 2H), 7.56 (d, 1H, J=3.8Hz), 7.56-7.66 (m, 3H), 8.67 (s, 1H).

Preparative Example 3 Preparation of Arylene 8

A catalytic amount of acetic acid was added to1,2-diamino-3,6-dibromobenzene and 4,4′-dimethoxybenzyl in butanol. Themixture was heated to 110° C. for 8 hours. The resulting mixture wasallowed to cool to room temperature, and filtered with washing(methanol), affording the arylene 8 as a red solid.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 3.85 (s, 6H), 6.90 (d, 2H, J=8.7 Hz),7.66 (d, 2H, J=8.7 Hz), 7.93 (s, 2H).

Preparative Example 4 Preparation of Oligothiophene Borolanes 10 and 11

3-Hexyl thiophene was reacted with N-bromosuccinimide (NBS) in aceticacid to obtain the compound 11a. Separately, n-BuLi was added to 3-hexylthiophene in tetrahydrofuran (THF) at −20° C., and thenN,N,N′,N′-tetramethylethylenediamine (TMEDA) was added thereto. Themixture was heated to 70° C. for 3 hours. Subsequently, dioxaborolanewas added to the mixture at −78° C. and was slowly allowed to warm toroom temperature to obtain the oligothiophene 10.

The compounds 11a and 10 were added to a mixture of toluene and water,and then tetrakis(triphenylphosphine)palladium (0) (Pd(PPh₃)₄, Aldrich)as a catalyst and potassium carbonate were added thereto. The reactionmixture was allowed to react at 110° C. for 8 hours to obtain thecompound 11b.

n-BuLi in tetrahydrofuran was added to the compound 11b at −20° C., andthen N,N,N′,N′-tetramethylethylenediamine (TMEDA) was added thereto. Themixture was heated to 70° C. for 3 hours. Subsequently, dioxaborolanewas added to the mixture at −78° C. and was slowly allowed to warm toroom temperature to afford the oligothiophene borolane 11.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.86-0.89 (m, 6H), 1.25-1.34 (m, 24H),1.58-1.63 (m, 4H), 2.60 (t, 2H, J=7.6 Hz), 2.74 (t, 2H, J=7.9 Hz), 6.90(s, 1H), 6.99 (s, 1H), 7.44 (s, 1H).

Preparative Example 5 Preparation of Oligothiophene Borolane 12

The oligothiophene borolane 12 was prepared in the same manner as inPreparative Example 4, except that 2-bromothiophene was used instead ofthe compound 11a.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.89 (t, 3H, J=6.8 Hz), 1.21-1.35 (m,18H), 1.59-1.66 (m, 2H), 2.58 (t, 2H, J=7.8 Hz), 6.68 (s, 1H), 7.00 (s,1H), 7.20 (d, 1H, J=3.5 Hz), 7.47 (d, 1H, J=3.5 Hz).

Preparative Example 6 Preparation of Oligothiophene Borolane 13

Thiophen-2-yl-magnesium bromide was added to a mixture of hexanal andTHF to obtain the compound 13a. Zinc iodide, sodium cyanoborohydride and1,2-dichloroethane were added to the compound 13a, and then the mixturewas heated to 85° C. for 3 hours to obtain the compound 13b. Lithiumdiisopropylamide (LDA) in THF was added to the compound 13b at −78° C.,and then dioxaborolane was added thereto to obtain the thiopheneborolane 10. Thereafter, the thiophene borolane 10 and2-bromobithiophene were subjected to the Suzuki coupling reaction underthe same conditions indicated in Preparative Example 1 to obtain thecompound 13c. Lithium diisopropylamide (LDA) in THF was added to thecompound 13c at −78° C., and then dioxaborolane was added thereto toafford the oligothiophene borolane 13.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.89 (t, 3H, J=6.8 Hz), 1.25-1.43 (m,18H), 1.57-1.88 (m, 2H), 2.79 (t, 2H, J=7.5 Hz), 6.68 (d, 2H, J=3.5 Hz),6.97-7.00 (m, 2H), 7.05 (d, 1H, J=3.5 Hz), 7.21 (d, 1H, J=3.5 Hz), 7.52(d, 1H, J=3.5 Hz).

Preparative Example 7 Preparation of Oligothiophene-Arylene Derivative 1

The arylene 6 and the oligothiophene borolane 11 were subjected tocondensation by the Suzuki coupling reaction to obtain the compound 1a.To the compound 1a was added N-bromosuccinimide to obtain the dibromide1b. The dibromide 1b and the oligothiophene borolane 13 were mixed withtoluene and water, and then Pd(PPh₃)₄, as a catalyst, and potassiumcarbonate in a solvent were added thereto. The resulting mixture washeated to 110° C. for 8 hours and washed with an aqueous ammoniumchloride solution. The obtained organic layer was distilled underreduced pressure and purified by silica gel column chromatography toafford the oligothiophene-arylene derivative 1.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.87-0.94 (m, 18H), 1.26-1.54 (m, 36H),1.65-1.90 (m, 12H), 2.78-2.91 (m, 12H), 6.69 (d, 2H, J=3.5 Hz), 7.00 (d,2H, J=3.5 Hz), 7.02 (d, 2H, J=3.5 Hz), 7.05-7.14 (m, 10H), 7.55-7.57 (m,4H), 7.78 (s, 2H), 8.02 (s, 2H). The ¹H-NMR spectra is illustrated inFIG. 2.

Preparative Example 8 Preparation of Oligothiophene-Arylene Derivative 2

The oligothiophene-arylene derivative 2 was prepared in the same manneras in Preparative Example 7, except that the compounds 10 and 12 wereused instead of the oligothiophene borolanes 11 and 13.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.90-0.93 (m, 18H), 1.30-1.48 (m, 36H),1.62-1.79 (m, 12H), 2.60 (t, 4H, J=7.7 Hz), 2.78 (t, 4H, J=7.7 Hz), 2.88(t, 4H, J=7.7 Hz), 6.82 (s, 2H), 7.03-7.08 (m, 8H), 7.10 (d, 2H, J=3.7Hz), 7.15 (s, 4H) 7.53 (d, 2H, J=3.7 Hz), 7.58 (d, 2H, J=3.7 Hz), 7.76(s, 2H), 8.00 (s, 2H).

Preparative Example 9 Preparation of Oligothiophene-Arylene Derivative 3

The arylene 7 and the oligothiophene borolane 11 were subjected tocondensation by the Suzuki coupling reaction to obtain the compound 3a.To the compound 3a was added N-bromosuccinimide to obtain the dibromide3b. The dibromide 3 b and the oligothiophene borolane 13 were mixed withtoluene and water, and then Pd(PPh₃)₄ as a catalyst and potassiumcarbonate in a solvent were added thereto. The resulting mixture washeated to 110° C. for 8 hours and washed with an aqueous ammoniumchloride solution. The obtained organic layer was distilled underreduced pressure and purified by silica gel column chromatography toafford the oligothiophene-arylene derivative 3.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.88-0.95 (m, 18H), 1.25-1.55 (m, 36H),1.66-1.88 (m, 12H), 2.78-2.98 (m, 12H), 6.68 (d, 2H, J=3.5 Hz),6.98-7.00 (m, 4H), 7.04-7.10 (m, 9H), 7.14 (s, 1H), 7.26-7.62 (m, 4H),7.76 (s, 1H), 8.47 (s, 1H), 8.96 (s, 1H).

Preparative Example 10 Preparation of Oligothiophene-Arylene Derivative4

The oligothiophene-arylene derivative 4 was prepared in the same manneras in Preparative Example 7, except that the arylene 9 was used insteadof the arylene 6.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.89-0.93 (m, 18H), 1.30-1.43 (m, 36H),1.68-1.82 (m, 12H), 2.77-2.87 (m, 12H), 6.69 (d, 2H, J=3.5 Hz),6.99-7.02 (m, 4H), 7.06-7.09 (m, 6H), 7.12 (d, 2H, J=3.5 Hz), 7.49 (s,2H), 8.81 (s, 2H).

Preparative Example 11 Preparation of Oligothiophene-Arylene Derivative5

The oligothiophene-arylene derivative 5 was prepared in the same manneras in Preparative Example 7, except that the arylene 8 was used insteadof the arylene 6 and that the thiophene borolanes 10 and 12 were usedinstead of the thiophene borolane 11.

¹H-NMR (300 MHz, CDCl₃) δ (ppm) 0.89-0.93 (m, 18H), 1.26-1.43 (m, 36H),1.64-1.88 (m, 12H), 2.80 (t, 12H, J=7.9 Hz), 3.88 (s, 6H), 6.69 (d, 2H,J=3.5 Hz), 6.95-7.12 (m, 10H), 7.22 (d, 2H, J=3.5 Hz), 7.77-7.82 (m,6H), 8.07 (s, 2H). The ¹H-NMR spectra is illustrated in FIG. 3.

Fabrication of OTFTs Example 1 Fabrication of Organic Thin FilmTransistor Using Oligothiophene-Arylene Derivative 1

As schematically illustrated in FIG. 1, first, chromium was deposited ona plastic substrate 1 that had been previously washed by a sputteringprocess to form a gate electrode 2 having a thickness of 1,000 Å, andthen SiO₂ was deposited on the gate electrode 2 by a CVD process to forma gate insulating film 3 having a thickness of 1,000 Å. ITO as amaterial for source-drain electrodes 4, 5 was deposited on the gateinsulating layer to a thickness of 1,200 Å by a sputtering process. Theresulting structure was washed with isopropyl alcohol for 10 minutes,dried, dipped in a 1 mM octadecyltrichlorosilane solution in hexane for30 seconds, washed with acetone, and dried. Separately, theoligothiophene-arylene derivative, compound 1, prepared in PreparativeExample 7 was dissolved in toluene to obtain a solution having aconcentration of 2 wt %. The solution was applied to the dried structureat 1,000 rpm to a thickness of 700 Å, and baked under an argonatmosphere at 100° C. for 1 hour to form an organic active layer 6 andfabricate an OTFT 7.

The current transfer characteristics of the organic thin film transistorfabricated in Example 1 using an oligothiophene-arylene derivativeprepared in Preparative Example 7 are graphically shown in FIG. 4.

Example 2

An organic thin film transistor was fabricated in the same manner as inExample 1, except that the oligothiophene-arylene derivative 2 preparedin Preparative Example 8 was used. The driving characteristics of thetransistor were measured.

Example 3

An organic thin film transistor was fabricated in the same manner as inExample 1, except that the oligothiophene-arylene derivative 3 preparedin Preparative Example 9 was used. The driving characteristics of thetransistor were measured.

Example 4

An organic thin film transistor was fabricated in the same manner as inExample 1, except that the oligothiophene-arylene derivative 4 preparedin Preparative Example 10 was used. The driving characteristics of thetransistor were measured.

Example 5

An organic thin film transistor was fabricated in the same manner as inExample 1, except that the oligothiophene-arylene derivative 5 preparedin Preparative Example 11 was used. The driving characteristics of thetransistor were measured.

The current transfer characteristics of an organic thin film transistorfabricated in Example 5 using an oligothiophene-arylene derivativeprepared in Preparative Example 11 are graphically shown in FIG. 5.

Comparative Example 1

An organic thin film transistor was fabricated in the same manner as inExample 1, except that polyhexylthiophene HT-P3HT (Aldrich) was used.

Evaluation of Electrical Properties of OTFTs

The charge carrier mobility of the devices fabricated in Examples 1-5and Comparative Example 1 was measured. The current transfercharacteristics of the devices were measured using a KEITHLEYsemiconductor characterization system (4200-SCS), and curves wereplotted. The obtained results are shown in Table 1. The charge carriermobility was calculated from the following current equations in thesaturation region.

The charge carrier mobility was calculated from the slope of a graphrepresenting the relationship between (I_(SD))^(1/2) and V_(G) from thefollowing current equations in the saturation region:

$I_{SD} = {\frac{{WC}_{0}}{2L}{\mu\left( {V_{G} - V_{T}} \right)}^{2}}$$\sqrt{I_{SD}} = {\sqrt{\frac{\mu\; C_{0}W}{2L}}\left( {V_{G} - V_{T}} \right)}$${slope} = \sqrt{\frac{\mu\; C_{0}W}{2L}}$$\mu_{FET} = {({slope})^{2}\frac{2L}{C_{0}W}}$

In the above equations, I_(SD): source-drain current, μ and μ_(FET):charge carrier mobility, C_(O): capacitance of the oxide film, W:channel width, L: channel length; V_(G): gate voltage, and V_(T):threshold voltage.

The off-state leakage current (I_(off)) is a current flowing in theoff-state, and was determined from the minimum current in the off-state.

TABLE 1 Charge carrier mobility Off-state leakage Organic active layer(cm²/Vs) current (A) Example 1 0.001 3 × 10⁻¹¹ Example 2 0.0003 1 × 10⁻⁹  Example 3 0.0002 1 × 10⁻¹⁰ Example 4 0.0004 1 × 10⁻⁹   Example 50.0004 1 × 10⁻¹⁰ Comparative Example 1 0.01 1 × 10⁻⁸   (HT-P3HT)

As can be seen from the data shown in Table 1, theoligothiophene-arylene derivatives of the present invention showed ahigh charge carrier mobility ranging from 0.001 to 0.0003 and aconsiderably low off-state leakage current.

As apparent from the foregoing, the oligothiophene-arylene derivativesof the present invention are low molecular weight organic semiconductormaterials with a novel structure. In addition, since theoligothiophene-arylene derivatives can be spin-coated at roomtemperature, are stable, and exhibit high charge carrier mobility andlow off-state leakage current, they can be used as a material for anactive layer of an OTFT.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims.

1. An organic thin film transistor comprising a substrate, a gateelectrode, a gate insulating film, an organic active layer andsource-drain electrodes wherein the organic active layer is made of theoligothiophene-arylene derivative according to an oligothiophene-arylenederivative of Formula 1:

wherein Ar is a C₂₋₃₀ heteroarylene interrupted by at least one nitrogenatom which may be substituted with hydrogen, hydroxyl, amino, a C₁₋₂₀linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl, alkylamino, esteror amido, or C₁₋₁₆ linear, branched or cyclic alkoxy, alkylamino, esteror amido; Ar₁ is a C₂₋₃₀ aryl group which may be interrupted by at leastone heteroatom and may be substituted with C₁₋₂₀ linear, branched orcyclic alkyl, Ar₂ is a C₅₋₃₀ aryl group which may be interrupted by atleast one heteroatom and may be substituted with hydrogen, hydroxyl,amino, C₁₋₂₀ linear, branched or cyclic alkyl, C₁₋₂₀ alkoxyalkyl,alkylamino, ester or amido, or C₁₋₁₆ linear, branched or cyclic alkoxy,alkylamino, ester or amido; the substituents R₁ are each independentlyhydrogen, hydroxyl, amino, C₁₋₂₀ linear, branched or cyclic alkyl, C₁₋₂₀alkoxyalkyl, alkylamino, ester, amido, or a C₁₋₁₆ linear, branched orcyclic alkoxy, alkylamino, ester or amido; n₁ is 1; n₂ is an integerbetween 2 and 8; and n₃ is an integer between 0 and
 6. 2. The organicthin film transistor according to claim 1, wherein the organic activelayer is formed into a thin film by screen printing, printing, spincoating, dipping, or ink spraying.
 3. The organic thin film transistoraccording to claim 1, wherein the insulating layer is made of aferroelectric insulator selected from the group consisting ofBa_(0.33)Sr_(0.66)TiO₃, Al₂O₃, Ta₂O₅, La₂O₅, Y₂O₃, and TiO₂; aninorganic insulator selected from the group consisting ofPbZr_(0.33)TiO_(0.66)O₃, Bi₄Ti₃O₁₂, BaMgF₄, SrBi₂(TaNb)₂O₉, Ba(ZrTi)O₃,BaTiO₃, SrTiO₃, Bi₄Ti₃O₁₂, SiO₂, SiN_(x), and AlON; or an organicinsulator selected from the group consisting of polyimides,benzocyclobutenes, parylenes, polyacrylates, polyvinylalcohols, andpolyvinylphenols.
 4. The organic thin film transistor according to claim1, wherein the substrate is made of a material selected from the groupconsisting of glass, polyethylenenaphthalate, polyethyleneterephthalate,polycarbonate, polyvinylalcohol, polyacrylate, polyimide,polynorbornene, and polyethersulfone.
 5. The organic thin filmtransistor according to claim 1, wherein the gate electrode andsource-drain electrodes are made of a material selected from the groupconsisting of gold, silver, aluminum, nickel, and indium tin oxide.